An early morning shooting left three armed guards dead and one in critical condition at a university campus in western Canada after an apparent robbery of an armored truck, police said Friday.

Police spokesman Scott Pattison said they continue to look for the shooter or shooters.

Pattison said no University of Alberta students were involved. The university was quickly put on lockdown, but that was later lifted.

G4S Cash Services spokeswoman Robin Steinberg confirmed two men and a woman were among the dead and were employees of the global security company. She said the guards were armed, but she did not have further details.

Steinberg said they've never had a fatality in Canada before.

"It's horrible to lose this many," she said.

Police called the shooting an attempted armed robbery. One G4S Cash Services van was found at the scene. Police also found an armored truck, running but abandoned, on the city's east side, not far from the G4S offices.

Such shootings are rare in Canada, where residents are nervous about anything that might indicate they are moving closer to their US counterparts. The oil boom town of Fort McMurray, Alberta, however, often has drug-related shootings, and Vancouver often has gang shootings. Gunfire at Toronto's most prominent mall this month left two dead and several injured. A shooting at an Edmonton club in 2006 left three dead.

Friday's shooting happened shortly after midnight in the Hub Mall area, which has student residences and shops. It's the university's summer session, so fewer students are living on campus.

Ian Breitzke, a student, said he was watching TV when he heard a man crying out in pain. He said when police came about 10 minutes later they broke down the door to a room behind an ATM and pulled out two people who looked dead.

The student said police then pulled out a man who was alive.

One photo posted to Facebook was taken from a balcony looking down into the mall. It shows three people lying in front of a TD Bank machine, with emergency crews working over them. Blood streaks the floor from behind the machine to where the bodies are.

Police were expected to give more details at a press conference later Monday.

"The university is saddened about those who lost their lives last night and we extend our condolences to their loved ones," the university said on its website.